We propose to continue the follow-up of the Nurses' Health Study II, a cancer epidemiology cohort of 116,430 women enrolled at ages 25 to 42 years in 1989. The cohort is currently supported as an R0I. Consistent with NCI policy, we are now applying for support of the infrastructure through a cooperative agreement. The NHSII biorepository includes plasma, red blood cells, white blood cells, and first morning urine samples from 29,611 women; for two thirds of these women we have timed follicular and luteal premenopausal samples. Over 16,000 provided a 2nd blood/urine sample in 2008-11 when the majorities were postmenopausal, and we have cheek cell DNA from an additional 29,859 women. We have collected archival tissue blocks for incident breast and ovarian cancers and melanoma (approximately 70% of requested have been obtained). We have created tissue microarrays for breast cancers that are already being used extensively. Prediagnostic mammograms have been collected for breast cancer cases and controls, as well as pathology material from previous biopsies of benign lesions. The follow-up of the NHSII cohort, conducted every two years, has been high and accounts for 93% of potential person-time. We have nearly complete ascertainment of deaths using the National Death Index and other methods. The NHSII cohort is unique in many ways, as the only large cohort of women enrolled before menopause, with information on smoking, weight, medication use, and medical diagnoses updated every 2 years and information on diet and physical activity updated every four years. Further, we have collected detailed on in utero and infant exposures (from participants' mothers), diet during high school, and other valuable exposure information. This cohort has been highly productive; over 150 papers have been published during the last five years, and the rate of publication is increasingly rapidly. This cohort is a member of the NCI Cohort Consortium, has participated in many collaborative studies, and has an active resource-sharing component. Enhancements of the cohort infrastructure involve assessment of breast tumor DNA methylation and RNA expression and the gut microbiome, and development of software to account for measurement error.